Semiconductor laser diode module

ABSTRACT

A semiconductor laser diode module in which a laser diode and an optical fiber are optically coupled with each other efficiently irrespective of an ambient temperature change within the laser diode module. The laser diode module includes a laser diode, an optical system including an optical fiber and a lens portion, a base configured to support the laser diode and at least a portion of the optical system, and a bottom plate configured to support the laser diode, the optical system, and the base. A portion of the base is made of a material having a first thermal expansion coefficient and the bottom plate is constructed of a material having a second thermal expansion coefficient, where the first thermal expansion coefficient is substantially equal to the second thermal expansion coefficient. The optical system is configured to receive and transmit a beam emitted from the laser diode through the lens portion to the optical fiber.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor laser diodemodule used in the field of optical communications.

[0003] 2. Discussion of the Background

[0004] With the explosive growth of the Internet and othercommunications needs, there has developed a commensurate need fortransmission systems to handle the ever increasing demand for capacityto transmit signals. Fiber optic systems have become the technology ofchoice for meeting this demand. Significant attention has been directedto systems which use dense wavelength division multiplexing (DWDM) toincrease the number of signal channels that can be transmitted through asingle optical fiber.

[0005] Semiconductor laser diodes have been used as a pumping lightsource for optical fiber amplifiers and as a signal light source in thefiber optic systems. The semiconductor laser diode module is a device inwhich a laser beam from the semiconductor laser diode is opticallycoupled with an optical fiber.

[0006] Erbium doped fiber amplifiers require 980 nm band and 1480 nmband semiconductor laser diode modules as pumping light sources. AndRaman amplifiers require 1350-1540 nm band semiconductor laser diodemodules as pumping light sources. 1550 nm band semiconductor laser diodemodules are well-known as the signal light source.

[0007] Optical coupling system between the laser diode and the opticalfiber is selected depending on a laser diode chip structure, the shapeof the mode-field of the light emitted from laser diode, and so on, toget higher optical coupling efficiency thereby.

[0008] The semiconductor laser diode module is required to have acertain quality of optical characteristics even at a higher ambienttemperature. The optical characteristics are represented by thestability of the optical coupling efficiency between laser diode and theoptical fiber, the stability of the output power from laser diode, andthe monitor current.

SUMMARY OF THE INVENTION

[0009] The present invention advantageously provides a laser diodemodule in which a laser diode and an optical fiber are optically coupledwith each other efficiently irrespective of an ambient temperaturechange within the laser diode module.

[0010] An embodiment of the present invention advantageously provides alaser diode module that includes a laser diode, an optical systemincluding an optical fiber and a lens portion, a base configured tosupport the laser diode and at least a portion of the optical system,and a bottom plate configured to support the laser diode, the opticalsystem, and the base. A portion of the base is made of a material havinga first thermal expansion coefficient and the bottom plate isconstructed of a material having a second thermal expansion coefficient,where the first thermal expansion coefficient is substantially equal tothe second thermal expansion coefficient. The optical system isconfigured to receive and transmit a beam emitted from the laser diodethrough the lens portion to the optical fiber.

[0011] The present invention provides a semiconductor laser diode modulehaving a base with a portion made of a material having a first thermalexpansion coefficient and a bottom plate constructed of a materialhaving a second thermal expansion coefficient which is substantiallyequal to the first thermal expansion coefficient. By providing that theportion of the base supported by the bottom plate, and the bottom platehave substantially equal thermal expansion coefficients, the laser diodemodule of the present invention provides a structure that is less proneto warping than the related art semiconductor laser diode module.Accordingly, the configuration of the present invention suppresses thedegradation in optical coupling efficiency between the laser diode andthe optical fiber due to the temperature change of the environmentalconditions of the semiconductor laser diode module.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A more complete appreciation of the invention and many of theattendant advantages thereof will become readily apparent with referenceto the following detailed description, particularly when considered inconjunction with the accompanying drawings, in which:

[0013]FIG. 1 is a cross-sectional view of a semiconductor laser diodemodule according to a first embodiment of the present invention;

[0014]FIG. 2 is a perspective view of the internal components of thefirst embodiment of the semiconductor laser diode module according tothe present invention;

[0015]FIG. 3 is a top view of the internal components of the firstembodiment of the semiconductor laser diode module according to thepresent invention;

[0016]FIG. 4 is an exploded, perspective view of a base of the firstembodiment of the semiconductor laser diode module according to thepresent invention;

[0017]FIG. 5 is a cross-sectional view of a holder mounting member ofthe first embodiment of the semiconductor laser diode module accordingto the present invention taken along line V-V in FIG. 4;

[0018] FIGS. 6(a), 6(b), 6(c), and 6(d) are perspective views ofalternative embodiments of fastening members of the first embodiment ofthe semiconductor laser diode module according to the present invention;

[0019] FIGS. 7(a) and 7(b) are side and top views, respectively, of alens portion of an optical fiber of the first embodiment of thesemiconductor laser diode module according to the present invention;

[0020] FIGS. 8(a) and 8(b) are perspective views of an arrangementregion of a laser diode and an arrangement region of a monitor photodiode, respectively, of the first embodiment of the semiconductor laserdiode module according to the present invention;

[0021]FIG. 9 is a perspective view of the internal components of asecond embodiment of the semiconductor laser diode module according tothe present invention;

[0022]FIG. 10 is a plan view of the internal components of the secondembodiment of the semiconductor laser diode module according to thepresent invention;

[0023]FIG. 11 is an exploded, perspective view of a base of the secondembodiment of the semiconductor laser diode module according to thepresent invention;

[0024] FIGS. 12(a) and 12(b) are cross-sectional, partial views of arelated art semiconductor laser diode module depicted in a non-operatingstate in FIG. 12(a), and in a operating state in FIG. 12(b) where themodule is depicted as being warped;

[0025] FIGS. 13(a) and 13(b) are schematic representations of therelated art semiconductor laser diode module depicting a non-operatingstate in FIG. 13(a), and an enlarged view of a portion of FIG. 13(a)depicting an optical coupling of the laser diode and optical fiber inFIG. 13(b);

[0026] FIGS. 14(a) and 14(b) are schematic representations of therelated art semiconductor laser diode module depicting a operating statein FIG. 14(a), and an enlarged view of a portion of FIG. 14(a) depictingan optical coupling of the laser diode and optical fiber in FIG. 14(b)where the non-operating state is depicted in phantom lines forcomparison;

[0027]FIG. 15 is a chart representing monitor tracking error based uponambient temperature changes in the related art semiconductor laser diodemodule and the semiconductor laser diode module according to the presentinvention;

[0028]FIG. 16 is a top view of a conceptual arrangement between a laserdiode, a lens portion and a structural support member of the presentinvention; and

[0029] FIGS. 17 (a) and (b) are side and top views of an alternativeembodiment of a lens portion of an optical fiber according to thepresent invention

DETAILED DESCRIPTION OF THE INVENTION Description of the Art forComparison

[0030]FIG. 12(a) depicts an example of a structure of a relatedsemiconductor laser diode module for comparison. The semiconductor laserdiode module depicted in FIG. 12(a) has a laser diode 1 for emitting alaser beam. The laser diode module includes an optical fiber 4 having alens portion 14 provided opposite a laser beam emitting end surface 31of the laser diode 1. The optical fiber 4 is accommodated in a sleeve 3made of metal. The optical fiber 4 receives and transmits the beamemitted from the laser diode 1 through the lens portion 14. The lensportion 14 has a wedge-shape.

[0031] The sleeve 3 is supported by fastening members 6 and 7, which aremounted on a base 2. The fastening members 6 and 7 are configured tosupport the optical fiber 4 through the sleeve 3 at intervals in alongitudinal direction of the optical fiber 4. The laser diode 1 ismounted on and fixed to laser diode bonding portion 21 on the base 2through a heat sink 22. A monitor photo diode 9 is mounted through amonitor photo diode carrier 39 to the base 2. The monitor photo diode 9monitors the optical output power of the laser diode 1. The base 2 ismounted on a thermo module 25.

[0032] The thermo module 25, the base 2, the laser diode 1, the opticalfiber 4 and the fastening members 6 and 7 are accommodated in a package27. The thermo module 25 is mounted on a bottom plate 26 of the package27. The bottom plate 26 of the package 27 is formed of a Cu—W alloy,specifically CuW20 (20% of Cu, 80% of W by weight). The thermo module 25has a base side plate member 17, a bottom plate side plate member 18,and peltier elements 19 clamped between the plate members 17 and 18. Thebase side plate member 17 and the bottom plate side plate member 18 ofthe thermo module 25 are both made of Al₂O₃.

[0033] The fastening members 6 and 7 and the base 2 are welded togetherby a known welding method, such as laser welding using a YAG laser, atlaser welding portions 10, and the fastening members 6 and 7 and thesleeve 3 are welded together at laser welding portions 11. The laserwelding portions 11 are formed at a higher position in a Y-direction inFIGS. 12(a) and 12(b) than that of the welding portions 10.

[0034] In the above-described semiconductor laser diode module, theoptical fiber 4 is aligned with the laser diode 1 so that the laser beamemitted from the laser diode 1 is received and transmitted in theoptical fiber 4 for use as desired. Also, in the semiconductor laserdiode module, when current for driving the laser diode 1 is turned on,the temperature of the laser diode 1 is increased by heat generationcaused by the current. The increase in temperature changes an opticaloutput power of the laser diode 1. Accordingly, during the operation ofthe semiconductor laser diode module, the temperature of the laser diode1 is monitored by a thermistor (not shown) fixed in the vicinity of thelaser diode 1, and the thermo module 25 is operated on the basis of themeasured temperature value. The thermo module 25 is operated such thatthe current through the thermo module 25 is controlled in an effort tomaintain a constant temperature of the laser diode 1 to keep the opticaloutput power of laser diode constant.

[0035] The inventors of the present invention have identified a problemwith the above-described semiconductor laser diode module. Theabove-described semiconductor laser diode module is configured such thatduring high temperature operation of the semiconductor laser diodemodule (for example, 40 to 50° C.), the base 2 is flexed due to thedifference in linear expansion coefficient between the base 2 and thebase side plate member 17 of the thermo module 25 due to the temperaturedifference therebetween. Accordingly, in the flexed state the positionsof the laser diode 1 and the optical fiber 4 are displaced from thealigned position, thereby degrading the optical coupling efficiencybetween the laser diode 1 and the optical fiber 4. Additionally, thesemiconductor laser diode module may be permanently deformed based uponthe flexing, and therefore the module may not fully regain properoptical coupling and the degradation in the optical coupling may be leftintact.

[0036] If the optical coupling efficiency between the laser diode 1 andthe optical fiber 4 is degraded in accordance with a change in ambienttemperature, then the light intensity of the beam received andtransmitted by the optical fiber 4 decreases, and it becomes impossibleto suitably operate the optical communication system to which thesemiconductor laser diode module is applied.

[0037] The inventors conducted a test on a semiconductor laser diodemodule as described above, and determined that a change in ambienttemperature causes warping of the base, which in turn causes an end ofthe optical fiber to shift with respect to the laser diode. FIGS. 13(a)and 13(b) are schematic representations of such a semiconductor laserdiode module depicting a lower ambient temperature state, i.e. 25° C.(room temperature) in FIG. 13(a), and an enlarged view of a portion ofFIG. 13(a) depicting an optical coupling of the laser diode and opticalfiber in FIG. 13(b). FIGS. 14(a) and 14(b) are schematic representationsof the semiconductor laser diode module of FIGS. 13(a) and 13(b)depicted in a higher ambient temperature state, i.e. 85° C. in FIG.14(a), and an enlarged view of a portion of FIG. 14(a) depicting anoptical coupling of the laser diode and optical fiber in FIG. 14(b). InFIG. 14(b), the configuration of FIG. 13(b) is depicted in phantom linesfor comparison.

[0038] As depicted in FIG. 13(b), in the lower ambient temperaturestate, the laser diode is a distance d₁ from the lens portion of theoptical fiber. As depicted in FIG. 14(b), in the higher ambienttemperature state the module warps such that the laser diode is adistance d₂ from the lens portion of the optical fiber. The change ofthe distance from d₁ to d₂ become longer, then the stability of opticalcharacteristics, for example, the stability of the optical couplingefficiency between laser diode and optical fiber, the stability ofoutput power from laser diode, and the stability of the monitor current,are more reduced. It is necessary to suppress the warping of the base soas to minimize the change of distance d₁ and d₂ for improvement of theseoptical characteristics.

Description of the Preferred Embodiments of the Invention

[0039] The present invention will now be described with reference topreferred embodiments that provide advantageous structures that overcomeproblems identified by the inventors, which are described above. In thedetailed description of the embodiments, the same reference numeralswill be used to indicate the same or similar components and a duplicatedexplanation will be omitted.

[0040] Referring now to the drawings, FIGS. 1-8(b) depict asemiconductor laser diode module according to a first embodiment of thepresent invention. As depicted in FIG. 1, the semiconductor laser diodemodule includes a package 27 configured to accommodate a laser diode 1,an optical fiber 4 having a lens portion 14, a sleeve or ferrule (ormore generally a holder) 3 for receiving therein the optical fiber 4, atleast one fastening means or fastening members 6 and 7 (7 a, 7 b) forsupporting the optical fiber 4 through the sleeve 3, a base 2 on whichthe fastening members 6 and 7 and the laser diode 1 are mounted directlyor indirectly, and a thermo module 25.

[0041] The base 2 according to the first embodiment is advantageouslyprovided with a laser diode mounting member 8 on which the laser diode 1is to be mounted, and a fastening means mounting member or holdermounting member 5 on which the fastening members 6 and 7 are to bemounted. The laser diode mounting member 8 is arranged on the thermomodule 25 in contact therewith, and as depicted in FIGS. 1, 2 and 4. Thelaser diode mounting member 8 has an upper portion with a laser diodebonding portion 21 formed integrally therewith, which defines a laserdiode mounting region. The holder mounting member 5 is disposed in aposition that does not interfere with the laser diode mounting region ofthe laser diode mounting member 8.

[0042]FIG. 4 is an exploded, perspective view of the base 2 includingthe holder mounting member 5 and the laser diode mounting member 8. Theholder mounting member 5 is fixed on an upper surface of the laser diodemounting member 8 on a brazing bonding portion 46 indicated by thehatching in FIG. 4. Note that in the preferred embodiment, portions ofthe holder mounting member 5 extend alongside the laser diode bondingportion 21.

[0043] The base 2 of the present invention is constructed of a laserdiode mounting member 8 that is advantageously formed of material havinga thermal expansion coefficient in a range between a thermal expansioncoefficient of the holder mounting member 5 and a thermal expansioncoefficient of a base side plate member 17 of the thermo module 25. Forexample, the laser diode mounting member 8 is preferably formed of aCu—W alloy, such as CuW10 (Cu of 10%, W of 90% by weight), having athermal expansion coefficient of about 6.5×10⁻⁶. Further, the holdermounting member 5 is preferably formed of an Fe—Ni—Co alloy, such asKovar®, having a thermal expansion coefficient in a range from 4.5×10⁻⁶to 5.1×10⁻⁶, and the base side plate member 17 of the thermo module 25is preferably formed of a material such as Al₂O₃, having a thermalexpansion coefficient of about 6.7×10⁻⁶.

[0044] During operation of the first embodiment of the laser diodemodule, a light beam is emitted from the laser diode 1 and is receivedand transmitted by the optical fiber 4. The thermo module 25 controlsthe temperature of the laser diode 1 during the operation of the laserdiode 1. In the present invention, the laser diode mounting member 8,which is in contact with the base side plate member 17 of the thermomodule 25, is advantageously made of material having a thermal expansioncoefficient in the range between the thermal expansion coefficient ofthe holder mounting member 5 provided on the upper side thereof and thethermal expansion coefficient of the base side plate member 17 (i.e., inthe present embodiment, CuW10 having the thermal expansion coefficientbetween that of Kovar® and that of Al₂O₃). By comparison, in the relatedart embodiment depicted in FIG. 12(a), the base 2, which is made ofmaterial having a low thermal expansion such as Kovar®, directlycontacts and the plate member 17 of the thermo module 25, which is madeof a material having a high thermal expansion coefficient such as Al₂O₃.Since the thermal expansion coefficients of adjacent contacting materialin the present invention gradually change, rather than substantiallyincreasing, as in the related art embodiment. The gradual increase inthe thermal expansion coefficients of adjacent contacting material inthe present invention reduces the warping or flexure of the base 2generated due to the temperature gradients created during operation ofthe laser diode. Accordingly, the present invention provides a structurethat suppresses the degradation in the optical coupling efficiencybetween the laser diode 1 and the optical fiber 4 due to the ambienttemperature change during operation of the laser diode module.

[0045] The present invention advantageously preferably provides that thethermal expansion coefficient of the laser diode mounting member 8 isequal to the thermal expansion coefficient of the bottom plate 26 of thepackage 27. For example, both the laser diode mounting member 8 and thebottom plate are preferably formed of a Cu—W alloy, such as CuW10.Accordingly, the same magnitude of stress is applied to both upper andlower sides of the thermo module 25 when the temperature change of thesemiconductor laser diode module is generated. Thus, the warping of thethermo module 25 is offset. Accordingly, the present invention providesa structure that effectively suppresses the degradation of the opticalcoupling efficiency between the laser diode 1 and the optical fiber 4due to an ambient temperature change.

[0046] The sleeve 3, the fastening members 6 and 7, and the holdermounting member 5 are preferably joined together by laser welding. It istherefore preferable to construct the sleeve 3, the fastening members 6and 7, and the holder mounting member 5 of a material that has lowthermal conductivity and a low thermal expansion coefficient, andtherefore has superior weldability, such as Kovar®. Additionally, theholder mounting member 5 is preferably made of a material havingsubstantially the same thermal expansion coefficient as that of theoptical fiber 4 and sleeve 3 in order to reduce any adverse effects onthe optical fiber 4 due to a difference in thermal expansioncoefficients. Accordingly, the present invention provides asemiconductor laser diode module that is easy to manufacture.

[0047] Additionally, in the present invention, the thermal conductivityof the laser diode mounting member 8 is advantageously preferably largerthan the thermal conductivity of the holder mounting member 5. Such aconfiguration provides an advantageous thermal heat path from the laserdiode 1 through the heat sink 22 and through the laser diode mountingmember 8 (without insulation from the holder mounting member 5) to thethermo module 25 and to the bottom plate 26, thereby providing for theefficient transfer of heat away from the laser diode 1 during operation.For example, as noted above, the laser diode mounting member 8 ispreferably formed of a Cu—W alloy, such as CuW10, and the holdermounting member 5 is preferably formed of an Fe—Ni—Co alloy, such asKovar®). The thermal conductivity of CuW10 is in the range of about 180to 200 W/mK, which is about ten times greater than the thermalconductivity of Kovar®, which is in the range of about 17 to 18 W/mK.

[0048] Accordingly, the present invention provides a heat pathconfiguration through the laser diode mounting member 8 of the base thatefficiently controls the temperature of the laser diode 1 using thethermo module 25, thereby allowing the laser diode 1 to operate at full,optimal power without the risk of overheating. The configuration of thepresent invention reduces the power consumption of the laser diodemodule as compared to the related art embodiment, since it allows thelaser diode 1 to operate at optimal power and allows the thermo module25 to efficiently transfer heat away from the laser diode withoutinsulation interference from the holder mounting member. Accordingly,the present invention advantageously provides a semiconductor laserdiode module that has small power consumption. Furthermore, the holdermounting member 5 of the present invention does not reach hightemperatures, as did the entire base of the related art module, andtherefore the overall warping of the base is reduced.

[0049] The holder mounting member 5 of the base 2 is provided togenerally extend in a longitudinal direction of the optical fiber 4 froman end portion on an optical fiber mounting side of the thermo module 25(i.e., at the right side of the thermo module 25 as depicted FIG. 1).Further, the holder mounting member 5 is provided on the upper surfaceof the laser diode mounting member 8. Additionally, the sleeve 3 holdingthe optical fiber 4 is fixed to the holder mounting member 5 andprojects from the end portion on the optical fiber mounting side of thethermo module 25. In this configuration, the projecting portion of theholder mounting member 5 is out of contact with the thermo module 25 andtherefore is not subjected to warping effects from the thermo module 25.Furthermore, since the sleeve 3 is fixed to the holder mounting member 5and projects from the thermo module 25, then the sleeve 3 is notsubjected to warping effects from the thermo module 25, thereby furthereffectively suppressing the reduction in optical coupling efficiencybetween the laser diode 1 and the optical fiber 4.

[0050] It should be noted that if the projection length L (see FIG. 1)of the holder mounting member 5 is too long, the bonding strength to thelaser diode mounting member 8 may be insufficient due to the weight ofthe projecting portion of the projection length L. Accordingly, there isa possibility that the bonding would be released if the projectingportion is subjected to vibration. Therefore, it is preferable toestablish a configuration where L<5 mm.

[0051] As depicted in FIG. 2, the laser diode mounting member 8preferably has a reinforcement portion 20 that extends under theprojecting portion of the holder mounting member, and further preferablyextends under the fastening member 6 located closer to the laser diode1. In the first embodiment, the reinforcement portion 20 has arectangular-parallelepiped shape. The reinforcement portion 20 supportsand braces the holder mounting member 5, whereby if vibration is appliedto the holder mounting member 5 in the Y-direction, then the effects ofthe vibration will be shifted to the laser diode mounting member 8. Sucha configuration will prevent vibration from adversely effecting theoptical coupling between the laser diode 1 and the optical fiber 4.Additionally, it is noted that the contact area between the holdermounting member 5 and the laser diode mounting member 8 can be increasedso that both components are more firmly and more mechanically fixedtogether. Furthermore, it should be noted that since the lower surfaceof the reinforcement portion 20 is out of contact with the thermo module25, then the reinforcement portion 20 is free from the adverse effectsof the warping of the thermo module 25.

[0052] As depicted in FIGS. 1 through 3, the fastening members 6 and 7are joined to the holder mounting member 5 at first joint portions orpositions 10, which are preferably formed using laser-weldingtechniques. The sleeve 3 is joined to the fastening members 6 and 7 atsecond joint portions or positions 11 (11 a, 11 b), which are alsopreferably formed using laser-welding techniques. The holder mountingmember 5 is used to support the fastening members 6 and 7, and thefastening members 6 and 7 are used to support the sleeve 3 and therebysupport the optical fiber 4. It should be noted that when the holdermounting member 5 and the fastening members 6 and 7 are welded togetherby laser beams, if the top surface of the holder mounting member 5 isflush with the top surface of the fastening members 6 and 7 (within ±100μm), it is possible to readily keep constant the height of the laserwelding portions 10 for every product.

[0053] The first joint positions 1 0 and the second joint positions 11are preferably located at substantially a same distance from the bottomplate 26. Preferably, the first joint positions 10 and the second jointpositions 11 are at substantially a same height in a directionperpendicular to the bottom plate 26, with a tolerance for a differencein height therebetween of within ±500 μm and more preferably within ±50μm. Preferably, the first joint positions 10 and the second jointpositions 11 are coplanar with the active layer of the laser diode 1,for example, the height of the first and second joint positions 10 and11 are at substantially the same height as the ridge line 14 a(refer toFIGS. 7(a),7(b)) of the optical fiber 4 which is opposite the activelayer of the laser diode 1.

[0054] The present invention advantageously provides at least one firstjoint position 10 joining the holder mounting member 5 of the base 2 andthe fastening members 6 and 7 of the optical fiber receiving sleeve 3,and at least one second joint position 11 joining the fastening members6 and 7 and the sleeve 3, where the first and second joint positions areformed to be at substantially the same height level in the directionperpendicular to the package bottom plate 26. Accordingly, even if thebase 2 is warped slightly, there is little possibility that the sleeve 3would be displaced about the pivot of the first joint position 10 due tothis warping. It is therefore possible to effectively suppress thedegradation of the optical coupling efficiency between the laser diode 1and the optical fiber 4.

[0055] In the first embodiment as depicted in FIGS. 3 and 5, at leastone structural support member or warping preventing means 15 is formedalong a longitudinal direction of the optical fiber 4 in the holdermounting member 5 of the base 2. The structural support member 15functions to prevent the warping of the base 2 by providing a portionhaving a thickness that provides structural integrity to the base 2. Inthis embodiment, the structural support member 15 is formed as a wallportion extending in a longitudinal direction of the optical fiber 4 andprovided upright on at least the upper side of a bottom portion 16 ofthe holder mounting member 5, as depicted in FIG. 5. In the firstembodiment, the structural support members 15 are formed integrally withthe holder mounting member 5. Therefore, there is no degradation inmechanical strength due to the connection between the structural supportmembers 15 and the holder mounting member 5, as compared with anembodiment where the structural support members 15 and the holdermounting member 5 are discretely formed to be adhered together.

[0056] The first embodiment advantageously includes a structural supportmember that extends along the longitudinal direction (Z-direction inFIG. 1) of the holder mounting member 5. Preferably, the structuralsupport member 15 is provided over a full region along the longitudinaldirection of the holder mounting member 5 (the region within the framesB indicated by the dotted lines in FIG. 3). Additionally, the structuralsupport member 15 is preferably formed on both sides of the holdermounting member 5 symmetrically about an optical axis of the opticalfiber 4, a portion 33 of the optical axis being depicted in FIGS. 3 and16 as extending to connect the laser beam emitting facet 31 of the laserdiode 1 and a laser beam receiving end 32 of the optical fiber 4. Thestructural support member 15 preferably includes portions that areformed on both sides of the fastening member 6 located closer to thelaser diode 1. Tip end portions of the structural support member 15extend to the region adjacent to the laser diode bonding portion 21 ofthe laser diode mounting member 8, such that the tip end portions areprovided on both sides of the laser diode bonding portion 21. The tipend portions adjacent the laser diode bonding portion 21 providerigidity to the region between the laser diode 1 and the optical fiber4, thereby maintaining efficient optical coupling. Therefore, thewarping of the base 2 in the region where the axial portion 33 and thefastening member 6 are arranged is effectively suppressed. The firstembodiment of the present invention thus effectively suppresses thewarping of the base 2 due to a temperature change during operation ofthe semiconductor laser diode module, thereby effectively suppressingdegradation in the optical coupling efficiency between the laser diode 1and the optical fiber 4.

[0057] As depicted in FIGS. 3 and 4, the holder mounting member 5includes fitting recess portions 37 for receiving the fastening members6 and 7. The fitting recess portions 37 are defined by the wall portionsconstituting the structural support members 15 and the wall portions 35for fastening the sides of the fastening members 6 and 7. The fasteningmembers 6 and 7 are welded and fixed at the first joint positions 10,such that the fastening members 6 and 7 are received within the fittingrecess portions 37. Incidentally, in the first embodiment, the wallportions 35 are part of the structural support members 15 and thereforeconstituting a warping preventing means. The wall portions 35 can beintegrally formed on the holder mounting member 5 by, for example,cutting away the fitting recess portions 37 for receiving the fasteningmembers 6 and 7 and an insertion portion for inserting the sleeve 3, asin the configuration depicted in FIG. 4.

[0058] The holder mounting member 5 has a U-shaped cross-sectional areataken along a plane transverse to the optical axis of the optical fiber,as depicted in FIG. 5. The structural support members 15 provide theside walls of the U-shaped cross-sectional area, and give the holdermounting member 5 structural integrity that prevents the warping of theholder mounting member 5. Alternatively, the holder mounting member 5can be formed with a different cross-sectional shape, such as anH-shape, etc.

[0059] Wall portions 35 extended to the laser diode side and the laserdiode bonding portion 21 also form together the U-shaped cross-sectionalarea around the laser diode 1 together.

[0060] As depicted in FIGS. 2 and 3, the fastening members 6 and 7 areseparated to support the sleeve 3 and the optical fiber 4 at differentpositions at intervals along the longitudinal direction of the opticalfiber 4. The fastening member 6 is located at the closest position (ascompared to the fastening member 7) to the laser diode 1 and ispreferably formed of an integral member with a clamping portion 28 forclamping the sleeve 3 and the optical fiber 4 at both sides. Thefastening member 6 preferably has a U-shaped cross-sectional area.

[0061] FIGS. 6(a), 6(b), 6(c), and 6(d) depict various embodiments offastening members that can be used either as fastening member 6 or asfastening member 7. Note that the embodiments depicted in FIGS. 6(a) and6(b) are preferably used as fastening member 6, since the clampingportions 28 of these embodiments are configured to be positioned asclose as possible to the laser diode 1, which allows for more precisealignment between the laser diode 1 and the optical fiber 4. Note thatthe embodiments depicted in FIGS. 6(c) and 6(d) are preferably used asfastening member 7, since the positioning of the clamping portions 28are not as crucial. The integrated fastening member 7 depicted in FIG.6(c) can be used advantageously to have a predetermined position andwidth of clamping portions 28. The fastening member 7 depicted in FIG.6(d) has the separate portions 7 a and 7 b that can clamp together thesleeve 3 tightly. Additionally, using an embodiment as depicted in FIG.6(a) is preferred, since the fastening member of FIG. 6(a) includes ajoint portion 49 that prevents warping of the base 2 in the X-direction,as compared with the a fastening member as depicted in FIG. 6(d), whichhas two separate fastening parts each supporting one side of the opticalfiber 4.

[0062] During the manufacturing process, the optical fiber 4 is movedaround the second joint positions 11 in order for the optical fiber 4 tobe optically coupled with the laser diode 1. Accordingly, if theclamping portions 28 of the fastening member 6 are formed to have anarm-shape as depicted in FIG. 6(b), then the stress applied to thesecond joint positions 11 when the optical fiber 4 is moved togetherwith the sleeve 3 around the second joint positions 11 is dispersed asdeformation stress on the arm of the clamping portion 28, thereby makingit possible to reduce the effect of stress concentrations.

[0063] The present invention includes an optical system that generallyincludes a lens portion and an optical fiber. In the first embodimentthe lens portion 14 is a wedge-shaped anamorphic (rotationallyasymmetric) lens integrated into the optical fiber 4 and having astructure depicted in FIGS. 7(a) and 7(b). In detail, ridge line 14 ahas a cylindrical surface. As depicted in FIGS. 2, 3 and 7, a ridge line14 a at a tip end faces a laser beam emitting face 31 of the laser diode1 such that the ridge line 14 a is in the same plane as an active layerof the laser diode 1. Although the optical fiber 4 preferably has ananamorphic, wedge-shaped lens portion 14 as depicted in FIGS. 7(a) and7(b), the optical fiber 4 can alternatively be constructed as ananamorphic lens portion other than the wedge-shape portion, or as afiber lens portion other than an anamorphic lens portion.

[0064] The shape of the fiber lens is not limited to a wedge shape. Analternative embodiment of the lens portion 14 is a conical shaped,rotationally symmetric lens (similar in shape to an end of a sharpenedpencil) that is integrated into the optical fiber 4, as depicted inFIGS. 17(a) and 17(b). More specifically, the tip of the cone of such afiber lens has a spherical surface. The fiber lens depicted in FIGS.17(a) and 17(b) is commonly called “a tapered lens ended fiber” or “asemi-spherically lensed fiber.”

[0065] Alternatively, the optical system can be constructed to have adiscrete lens supported by the holder mounting member 5, an opticalisolator supported by the holder mounting member 5, a second lenssupported by the package 27, and an optical fiber supported by thepackage 27. In this configuration, the lens portion 14 is constructed asa discrete lens portion from the optical fiber 4 such that the discretelens portion, the optical isolator, and the second lens are providedbetween the laser diode 1 and the tip end of the optical fiber 4. Insuch a configuration, the optical isolator is preferably mounted using amaterial having minimal magnetic properties, such as SUS 430, in orderto reduce interference with the optical isolator.

[0066] As depicted in FIG. 8(a), the laser diode 1 is preferably fixedon the heat sink 22 by, for example, AuSn or AuSi solder, and the heatsink 22 is fixed on the laser diode mounting member 8 by, for example,AuSn or AuSi solder. The heat sink 22 is preferably formed of materialof high thermal conductivity such as AlN or diamond. As depicted in FIG.8(b), the monitor photo diode carrier 39 is fixed on the laser diodemounting member 8 of the base 2 by soldering material 43. The monitorphoto diode carrier 39 is preferably formed mainly of alumina. An Auplating pattern 50 is formed on the surface of the monitor photo diodecarrier 39. The photo diode 9 is fixed on the plating pattern 50 bysoldering material 44, such as AuSn.

[0067]FIGS. 9 and 10 depict the internal components of a secondembodiment of the semiconductor laser diode module according to thepresent invention, where the thermo module 25 and the package 27 havebeen omitted. FIG. 11 is an exploded, perspective view of a base 2 ofthe second embodiment of the semiconductor laser diode module accordingto the present invention.

[0068] The second embodiment enjoys substantially the same advantages asthose of the above-described first embodiment. The feature of the secondembodiment that is different from the first embodiment is the uniqueshapes of the holder mounting member 5 and the laser diode mountingmember 8 which constitute the base 2. More specifically, in the secondembodiment the structural support members 15 are formed on both theholder mounting member 5 and the laser diode mounting member 8. Thestructural support members 15 are provided on both sides of the axialportion 33 connecting the laser beam emitting facet 31 of the laserdiode 1 and the laser beam receiving end 32 of the optical fiber 4 andon both sides of the fastening member 6 located closer to the laserdiode 1. The structural support members 15 are preferably formedintegrally with the holder mounting member 5 and integrally with thelaser diode mounting member 8.

[0069] The present invention is not limited to the above-describedembodiments but may take various forms. The following discussiondescribes various exemplary alternative configurations of the presentinvention.

[0070] The laser diode module according to the present inventionpreferably includes a thermo module 25 in order to control thetemperature of the laser diode 1, as described above. However, the laserdiode module of the present invention can be constructed without athermo module, such that the base 2 is supported by or integrated intothe bottom plate 26. Such a configuration is required, for example, inundersea application due to the suppression of electric powerconsumption.

[0071] The first and second embodiments depict structural supportmembers 15 that are formed as wall portions extending in thelongitudinal direction of the optical fiber and provided upright on anupper side of the holder mounting member 5 or the laser diode mountingmember 8. However, the configuration of the structural support members15 is not limited to the specific shape depicted in the figures, butrather can be configured in alternative shapes, for instance,rod-shaped, or angular shaped one, which are attached to the base 2 by,for example, adhesives or solder.

[0072] Furthermore, in each of the foregoing embodiments, the holdermounting member 5 of the base 2 is preferably provided to project in thelongitudinal direction of the optical fiber 4 from the end portion onthe optical fiber mounting side of the laser diode mounting member 8.However, it is not necessary to provide the holder mounting member 5 ofthe base 2 so as to project from the laser diode mounting member 8 asdescribed above. Other configurations can be used as will be readilyapparent to one of skill in the art based upon the teaching set forthherein.

[0073] In each of the foregoing embodiments, the laser diode mountingmember 8 preferably has a reinforcement portion 20 formed under thefastening member 6 located on the closest side to the laser diode 1.Alternatively, it is possible to dispense with the reinforcement portion20. However, since the reinforcement portion 20 is provided to suppressthe vibration of the holder mounting member 5 in the Y-direction of thedrawings, it is preferable to provide the reinforcement portion 20.Furthermore, the configuration of the reinforcement portion 20 is notlimited to any particular shape, but rather may be selected as desired.For instance, the reinforcement portion 20 may take a structure having atapered surface, as indicated by phantom lines A in FIG. 2.

[0074] Although the laser diode mounting member 8 and the bottom plate26 of the package 27 of the preferred embodiments are made of the samematerial to have the same thermal expansion coefficient, it is possibleto use different materials for the laser diode mounting member 8 and thebottom plate 26. However, in this configuration it is preferable if thethermal expansion coefficients of the different materials aresubstantially the same.

[0075] The present invention provides a structure that advantageouslyreduces any degradation in the optical characteristics, i.e. the opticalcoupling efficiency of the laser diode module, due to the changes in theambient temperature of the module. As described earlier with respect toFIGS. 7(a) and 7(b), the optical fiber 4 of the first embodiment has thewedge-shaped lens portion 14 with the ridge line 14 a at a tip end inparallel with the X-Z plane. The optical coupling between the lensportion 14 of the optical fiber 4 and the laser diode 1 is susceptibleto adverse effects of positional displacement, in particular, in theY-direction if bending of the module occurs, as seen with respect to therelated embodiment depicted in FIGS. 12(a), 12(b), 13(a), 13(b), 14(a),and 14(b).

[0076] When the base 2 is warped along the longitudinal direction of theoptical fiber 4, the degradation in optical coupling efficiency betweenthe laser diode 1 and the optical fiber 4 is likely to significantlyoccur. However, in accordance with the first embodiment of the presentinvention, the warping of the base 2 along the longitudinal direction ofthe optical fiber 4 is suppressed by the structural support members 15,thereby the stability of the optical coupling efficiency between thelaser diode 1 and the optical fiber 4.

[0077] In the first and second embodiments, since the light emitted fromthe laser diode 1 is introduced from the tip end side of the opticalfiber 4 into the optical fiber 4, it is important to suppress thepositional displacement between the laser diode 1 and a laser beamreceiving end 32 of the optical fiber 4. It is therefore important tosuppress the warping of the base 2 at the axial portion 33.Additionally, a displacement in the fastened position of the sleeve 3 bythe fastening member 6 will cause a greater degradation in couplingefficiency as compared to that by the fastening member 7, which islocated further from the laser diode 1 than the fastening member 6.Therefore, it is important to suppress the warping of the base 2 in theregion where the fastening member 6 is arranged. The present inventionachieves such an advantageous structure.

[0078]FIG. 15 is a chart representing monitor tracking error based uponambient temperature changes in the semiconductor laser diode module ofthe related art and of the present invention. The monitor tracking erroris defined as ΔIm=(Im(T)−Im(25° C.))/Im(25° C.). In the laser diodemodule according to the present invention, since the warping of the baseis suppressed, the sinusoidal change in the back-facet monitor currentdue to the change in ambient temperature is suppressed. As depicted inFIG. 15, the tracking error (ΔIm) of the laser diode module of thepresent invention appears to change with a longer period than therelated art laser diode module, which demonstrates that the variouswarping prevention means of the present invention function to preventthe displacement of the fiber-end with respect to the laser diode.

[0079] It should be noted that the exemplary embodiments depicted anddescribed herein set forth the preferred embodiments of the presentinvention, and are not meant to limit the scope of the claims hereto inany way.

[0080] According to a first aspect of the present invention, since thebase is formed by the laser diode mounting member contacted and disposedon the thermo module and by the holder mounting member on the upper sidethereof, with the laser diode mounting member being formed of materialhaving a thermal expansion coefficient in a range between a thermalexpansion coefficient of the holder mounting member and a thermalexpansion coefficient of the base side plate member of the thermomodule, the present invention advantageously suppresses the warping ofthe base caused by the temperature change in the environmentalcircumstances of the semiconductor laser diode module in comparison withthe related art module. Accordingly, the present inventionadvantageously suppresses the degradation in optical coupling efficiencybetween the laser diode and the optical fiber due to the temperaturechange of the environmental circumstances of the semiconductor laserdiode module.

[0081] According to a second aspect of the invention, since the base isformed by the laser diode mounting member contacted and disposed on thethermo module and by the holder mounting member, with the thermalexpansion coefficients of the laser diode mounting member and the bottomplate of the package being substantially equal to each other, the samemagnitude of stress is applied on both upper and lower sides of thethermo module when the temperature change of the semiconductor laserdiode module is generated. Therefore, the present inventionadvantageously offsets the warping of the thermo module and suppressesthe degradation in optical coupling efficiency between the laser diodeand the optical fiber due to the ambient temperature change.

[0082] According to a third aspect of the invention, since a first jointposition obtained by laser-welding together the holder mounting memberand the fastening members of the sleeve for holding the optical fiberand a second joint position obtained by laser-welding together thefastening members and the sleeve are formed to be at substantially thesame height level in a direction perpendicular to a bottom plate of thepackage, even if warping is generated in the base to some extent, thereis no significant positional displacement of the sleeve corresponding tothe warping. Accordingly, the present invention advantageouslysuppresses the degradation in optical coupling efficiency between thelaser diode and the optical fiber.

[0083] According to a fourth aspect of the invention, since a structuralsupport member for preventing the warping of the base is provided on thebase in a longitudinal direction of the optical fiber on at least oneside of the optical fiber, the warping of the base is suppressed by thestructural support members. Accordingly, the present inventionadvantageously suppresses the degradation in optical coupling efficiencybetween the laser diode and the optical fiber.

[0084] According to a fifth aspect of the invention, since a structuralsupport member is provided on at least one side of an axial portionconnecting a laser beam emitting facet of the laser diode and a laserbeam receiving end of the optical fiber, warping at the axial portion issuppressed and the degradation in optical coupling efficiency betweenthe laser diode and the optical fiber is efficiently suppressed.Accordingly, the present invention advantageously suppresses thedegradation in optical coupling efficiency between the laser diode andthe optical fiber.

[0085] According to a sixth aspect of the invention, since a structuralsupport member is provided on at least one side of the fastening memberlocated on the closest side to the laser diode (i.e., in a region alongthe longitudinal direction of the optical fiber of the holder mountingmember including at least one side), warping of the base in the regionof the fastening member that is most likely to affect the degradation inoptical coupling efficiency between the laser diode and the opticalfiber is suppressed.

[0086] According to a seventh aspect of the invention, since astructural support member is formed integrally with the holder mountingmember, it is possible to avoid a reduction in mechanical strength dueto the connection between a structural support member and a discreteholder mounting member. Thus, it is possible to effectively prevent thewarping of the base by the structural support members, and toeffectively suppress the degradation in optical coupling efficiencybetween the laser diode and the optical fiber.

[0087] According to an eighth aspect of the invention, since thestructural support member is preferably formed with a wall portionextending in a longitudinal direction of the optical fiber, and providedupright at least on an upper side of the holder mounting member, it ispossible to provide means for effectively suppressing the warping of thebase with a simple structure. Accordingly, the present inventionadvantageously suppresses the degradation in optical coupling efficiencybetween the laser diode and the optical fiber.

[0088] According to a ninth aspect of the invention, since the fasteningmember for supporting and fastening the optical fiber in the closestside to the laser diode is formed of an integral part provided with aclamping portion for clamping both sides of the optical fiber, it ispossible to suppress the warping of the base in the horizontal directionintersecting with the longitudinal direction of the optical fiber incomparison with a case where separate fastening members support eachside of the optical fiber. Accordingly, the present inventionadvantageously suppresses the degradation in optical coupling efficiencybetween the laser diode and the optical fiber.

[0089] According to a tenth aspect of the invention, since the base isprovided to project in the longitudinal direction of the optical fiberfrom end portion of the thermo module on the optical fiber mountingside, it is possible to suppress the phenomenon that the portion that isout of contact with the thermo module (i.e., the projection portion ofthe base) is subjected to the adverse effect of the warping of thethermo module. Thus, a fastening member of the optical fiber is mountedin this region to thereby make it possible to effectively suppress thedegradation in optical coupling efficiency between the laser diode andthe optical fiber.

[0090] According to an eleventh aspect of the invention, since theholder mounting member of the base is provided to project in thelongitudinal direction of the optical fiber from the end portion of thelaser diode mounting member on the optical fiber mounting side, it ispossible to suppress the phenomenon that this portion is subjected tothe adverse effect of the warping of the laser diode mounting member.Thus, a fastening member of the optical fiber is mounted in thisprojected region to thereby make it possible to effectively suppress thedegradation in optical coupling efficiency between the laser diode andthe optical fiber.

[0091] According to a twelfth aspect of the invention, since the laserdiode mounting member of the base has a reinforcement portion formedunder the fastening member located in the closest position to the laserdiode, even if the vibration in the direction perpendicular to thepackage bottom plate is applied to the holder mounting member, anypivoting caused by the vibration will be farther from the laser diodethan the fastening member. Additionally, the lower surface of thereinforcement portion is out of contact with the thermo module wherebyit is possible to suppress the adverse effect of the warping of thethermo module against the reinforcement portion.

[0092] According to a thirteenth aspect of the invention, since theholder mounting member, the fastening members and the structural supportmembers are preferably made of Kovar® or a similar material, it ispossible to manufacture a semiconductor laser diode module with highworkability/weldability. Additionally, Kovar® advantageously hassubstantially the same thermal expansion coefficient as that of theoptical fiber, and thus adverse effects on the optical fiber due to thedifference in thermal expansion coefficient between the optical fiber,and the holder mounting member and the structural support member aresuppressed.

[0093] Numerous modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

What is claimed is:
 1. A laser diode module comprising: a laser diode;an optical system including an optical fiber and a lens portion, saidoptical system being configured to receive and transmit a beam emittedfrom said laser diode through said lens portion to said optical fiber; abase configured to support said laser diode and at least a portion ofsaid optical system; and a bottom plate configured to support said laserdiode, said optical system, and said base, wherein a portion of saidbase is made of a material having a first thermal expansion coefficientand said bottom plate is constructed of a material having a secondthermal expansion coefficient, and wherein said first thermal expansioncoefficient is substantially equal to said second thermal expansioncoefficient.
 2. The laser diode module according to claim 1, whereinsaid portion of said base and said bottom plate are made of a samematerial.
 3. The laser diode module according to claim 1, wherein saidportion of said base is coupled to said bottom plate via a temperaturecontrol device.
 4. The laser diode module according to claim 3, whereinsaid temperature control device is a thermo module, said thermo modulecomprising a first plate member attached to said portion of said base, apeltier element attached to said first plate member, and a second platemember attached to said peltier element and said bottom plate.
 5. Thelaser diode module according to claim 4, wherein said first plate memberis made of a material having a first thermal expansion coefficient andsaid second plate member is constructed of a material having a secondthermal expansion coefficient, and wherein said first thermal expansioncoefficient is substantially equal to said second thermal expansioncoefficient.
 6. The laser diode module according to claim 4, whereinsaid first plate member and said second plate member are made of a samematerial.
 7. The laser diode module according to claim 1, wherein saidbase comprises an optical system mounting member configured to supportsaid optical fiber, and wherein said portion of said base is a laserdiode mounting member configured to support said laser diode, saidoptical system mounting member being attached to said laser diodemounting member.
 8. The laser diode module according to claim 7, whereinsaid optical system mounting member is formed of an Fe—Ni—Co alloy. 9.The laser diode module according to claim 1, wherein said lens portionhas a fiber lens formed on said optical fiber, and wherein a tip endside of said fiber lens and a light emitting facet of said laser diodeare arranged to oppose each other.
 10. The laser diode module accordingto claim 9, wherein said fiber lens is an anamorphic lens.
 11. The laserdiode module according to claim 1, wherein said bottom plate is a partof a package configured to accommodate said laser diode.
 12. Asemiconductor laser diode module comprising: a laser diode; an opticalsystem including an optical fiber and a lens portion, said opticalsystem being configured to receive and transmit a beam emitted from saidlaser diode through said lens portion to said optical fiber; a fasteningmeans for supporting at least a portion of said optical system; a baseconfigured to support said fastening means and said laser diode, saidbase includes a laser diode mounting member and a fastening meansmounting member, said laser diode mounting member having a laser diodemounting region configured to mount said laser diode, said fasteningmeans mounting member being mounted to said laser diode mounting memberat a position other than said laser diode mounting region; and a bottomplate configured to support said laser diode, said optical system, saidfastening means, and said base, wherein said bottom plate is made ofmaterial having a linear expansion coefficient that substantially equalto a linear expansion coefficient of said laser diode mounting member.13. The semiconductor laser diode module according to claim 12, furthercomprising a thermo module including a first plate member attached tosaid laser diode mounting member, a peltier element attached to saidfirst plate member, and a second plate member attached to said peltierelement and said bottom plate; and a package for accommodating thereinsaid laser diode, said optical system, said fastening means, said baseand said thermo module.
 14. The semiconductor laser diode moduleaccording to claim 12, wherein said base projects in a directionparallel to an optical axis of said optical system from an end portionon an optical fiber mounting side of said thermo module.
 15. Thesemiconductor laser diode module according to claim 14, wherein saidfastening means mounting member projects in a direction parallel to saidoptical axis from an end portion on an optical fiber mounting side ofsaid laser diode mounting member.
 16. The semiconductor laser diodemodule according to claim 15, wherein said laser diode mounting memberhas a reinforcement portion configured to mechanically reinforce saidfastening means mounting member located in a closest position to saidlaser diode, and wherein said reinforcement portion has a lower surfacethat is out of contact with said thermo module.
 17. The semiconductorlaser diode module according to claim 12, wherein said lens portion hasa fiber lens formed on said optical fiber, and wherein a tip end side ofsaid fiber lens and a light emitting facet of said laser diode arearranged to oppose each other.
 18. The semiconductor laser diode moduleaccording to claim 17, wherein said fiber lens is an anamorphic lens.19. The semiconductor laser diode module according to claim 12, whereinsaid fastening means is formed of an Fe—Ni—Co alloy.
 20. Thesemiconductor laser diode module according to claim 12, wherein saidfastening means mounting member is formed of an Fe—Ni—Co alloy.